NEW YORK (BLOOMBERG) - Pfizer Inc Chief Executive Officer Albert Bourla said that a key safety milestone had been reached in the study of its Covid-19 vaccine, and the drugmaker is now preparing to seek an emergency-use authorisation from US regulators.

Speaking at a virtual conference hosted by the New York Times on Tuesday (Nov 17), Mr Bourla said the company was preparing to submit its data to the US Food and Drug Administration (FDA).

Last week, Pfizer and its partner BioNTech SE reported that an interim analysis showed their experimental vaccine was more than 90 per cent effective in preventing symptomatic cases of Covid-19.

"We are preparing now for submissions," Mr Bourla said at the conference without specifying when it anticipated to file for an emergency use authorisation.

Nonetheless, Mr Bourla added, important questions about the vaccine still remain to be answered. "When it comes to how durable the protection could be, this is something we don't know yet," he said.

Mr Bourla added that Pfizer would soon release more detailed efficacy results.

Pfizer shares were up 1.6 per cent at 3.22pm in New York.

Pfizer and BioNTech had been working to accumulate two months of follow-up safety data on volunteers who had received the full two-dose regimen of their vaccine. The FDA requires the information for emergency clearance.

The safety data is one of the last hurdles needed before Pfizer and BioNTech can apply for emergency authorisation.

The New York-based drug giant will continue to monitor trial participants well after any authorisation or approval in order to assure that safety concerns don't crop up later, Mr Bourla said.

The Pfizer-BioNTech vaccine is slightly ahead of one from Moderna Inc in the race to the finish line.

Moderna announced Monday that its own candidate was 94.5 per cent effective. Moderna expects to get the safety data it needs by the end of the month, allowing it to file for emergency clearance in the coming weeks.

Mr Bourla said at the New York Times conference that Pfizer had not been overly specific when it reported "more than 90 per cent efficacy" because that number was likely to fluctuate as the trial gained more cases. The company will report out an additional number once it publishes fuller data, he said.

The drug industry executive spoke alongside Mr Bill Gates and Ms Heidi Larson, director of the Vaccine Confidence Project, in a discussion about vaccine development, distribution and uptake.

The most recent trial results are "a glorious confirmation of the power of the technology," Mr Bourla said, referring the the novel messenger RNA used in Pfizer and BioNTech's vaccine.

Mr Bourla's tenure at Pfizer spans more than 27 years. He said at a later conference held Tuesday by the online media publication STAT that it was one of the best days of his life when he learned of the vaccine's success.

"You're relieved because the news that you're expecting to hear will not only determine the future of the company, but the future of your world," Mr Bourla said. "I felt that I was living a dream."

At other times throughout the pandemic, the company has faced political tumult and scrutiny, Mr Bourla said.

The Pfizer chief rebutted concerns that he sought to report the effectiveness of the vaccine before Election Day, potentially influencing the outcome of the US presidential vote.

"I did not have any political or any artificial timelines in my mind," Mr Bourla said. Instead, at the start of the company's work on the vaccine, he set an October goal after his scientists said the product would only be ready by mid-2021.

He pushed for the earlier date, he said, to have a vaccine ready for a possible winter surge of infections.

"I said, 'Go back and see how many people would die'" if there were a new spike in cases. But the October timeline became publicly conflated with President Donald Trump's political ambitions.

Mr Bourla said he didn't take US taxpayer dollars for the vaccine's research and development in order to avoid politics that might be attached to the effort.

"When you want to go from the middle of next year to the middle of October, you need to remove any bureaucracy," he said. "And I knew this would become very political."